This could 100% be my personal bias, as I am often the one that's elbow-deep in SDL's audio subsystem, but when porting SDL to a new platform, I find starting with audio to be the easiest. Generally it'll work without any sort of GUI components wired up (or video at all!), so once the base library is compiling, filling in an audio backend and figuring out how to coerce loopwave.c to run on the device is usually the first step.